Optical membrane heating and temperature control method and apparatus
Methods and systems for heating a space deployed membrane assembly are provided. The membrane assembly can include one or more framed sections. Each section can include a composite membrane having a membrane substrate and a transparent, electrically conductive resistive coating. The composite membrane is held within a frame. Electrically conductive bus bars are provided and are placed in intimate electrical contact with the resistive coating. The electrically conductive bus bars are generally arranged, on opposite sides of the perimeter of the membrane. A controller passes current between selected bus bars, with different bus bars operative to pass current between them at different times. The magnitude of the voltage applied to the bus bars, the location of the bus bars, the operational sequence of powering the bus bars, and the time over which current is passed between a selected pair of bus bars, are selected to provide substantially uniform time averaged heating of the membrane.
1. A membrane section, comprising:
a frame;
a composite membrane, including:
a membrane substrate, wherein the membrane substrate includes diffractive elements; and
an electrically conductive layer, wherein the composite membrane is held within a perimeter of the frame;
at least two bus bars, wherein the at least two bus bars are electrically connected to the electrically conductive layer of the composite membrane.
2. The membrane section of claim 1 , wherein the frame includes at least four sides, and wherein at least two bus bars are electrically connected to the composite membrane at each of the four sides, whereby the membrane section includes at least eight bus bars.
3. The membrane section of claim 2 , wherein at least one of the at least four sides has a different length than at least three of the at least four sides.
4. The membrane section of claim 1 , wherein the electrically conductive layer is transparent to light within at least a first range of wavelengths.
5. The membrane section of claim 1 , wherein the diffractive elements include a pattern of variations in a thickness of the membrane substrate.
6. The membrane section of claim 1 , wherein the diffractive elements include a pattern of variations in an optical transmission characteristic of the membrane substrate.
7. The membrane section of claim 1 , wherein the electrically conductive layer is an electrically conductive coating.
8. The membrane section of claim 1 , wherein the membrane substrate includes an optical coating comprising the diffractive elements.
9. A method for heating a section of a membrane assembly, comprising:
passing an electrical current across at least a first portion of a composite membrane included in the section during a first period of time between at least first and second bus bars electrically connected to the composite membrane, wherein the composite membrane includes diffractive elements, wherein the composite membrane is electrically conductive, and wherein passing an electrical current across at least the first portion of the composite membrane raises a temperature of the first portion of the composite membrane;
passing an electrical current across at least a second portion of the composite membrane included in the section during a second period of time between at least third and fourth bus bars electrically connected to the composite membrane, wherein passing an electrical current across at least the second portion of the composite membrane raises a temperature of the second portion of the composite membrane.
10. The method of claim 9 , wherein the composite membrane is held within a frame, wherein the frame defines a perimeter of the membrane, and wherein the bus bars are not electrically connected to the frame.
11. The method of claim 10 , wherein a perimeter of the composite membrane held within the frame is not rectangular.
12. The method of claim 9 , wherein the first and second bus bars are on first and second sides of the perimeter of the composite membrane respectively.
13. The method of claim 12 , wherein the first and second sides of the perimeter of the composite membrane are opposite one another.